Iran has stepped up its already tough Internet censorship policy by blocking the most popular antifiltering tool used by Iranians to access blocked websites. Beginning last week, Iranian authorities began blocking virtual private networks (VPNs), which an estimated 30 percent of the country's Internet users employ to get around state censorship.

Communications tools that allow free phone calls, like Skype and Viber, and free text messaging, like WhatsApp, have also reportedly been disrupted.

The move, which was first reported by citizen journalists, was confirmed March 10 by Ramezanali Sobhani-Fard, the head of parliament's Information and Communications Technology Committee.

"Within the last few days, illegal VPN ports in the country have been blocked," Sobhani-Fard declared, adding that from now on only “legal and registered VPNs” may be used.

The ban puts in place an even higher hurdle for Iranians hoping to escape state censorship online.

VPNs allow millions of Iranians to gain access to the Internet via networks based outside the country. They can then visit the thousands of websites that are blocked in Iran for being deemed immoral or against the country’s national security.

“These days, when one manages to log on to Facebook, it feels like being [Soviet space pioneer] Yuri Gagarin,” reads a joke posted on a popular satirical Facebook page.

Washington-based independent Internet researcher Collin Anderson told RFE/RL that Iran’s decision to target the most widely used and secure antifiltering tool signals a ratcheting-up by the regime of control over what Iranians can see and say.

Anderson says the regime is being selective about which VPNs to shut down so as not to hurt the struggling Iranian economy. In addition to private citizens who are seeking uncensored content, VPNs are also widely used by businesses, media, and researchers.

“I think what they want to do is they want to differentiate which of the VPNs are being used by an international business so that when they need to turn all of the VPNs off, they only turn off the ones that are being used by people trying to bypass the filter," Anderson says. "So they’re trying to differentiate [between] VPNs so they have less of an economic [impact] every time they censor the Internet."

Authorities are advising Iranians to purchase “legal, registered VPNs,” but the journalist watchdog group Reporters without Borders (RSF) says that will give authorities even more ability to spy on people’s Internet activities.

In a new report out March 11, the group names Iran one of the five biggest state enemies of the Internet for its practice of monitoring citizens’ online activity and intercepting electronic communication in order to arrest journalists and dissidents.

Of the regime’s efforts to get Iranians to buy “registered” VPNs, RSF says: "The VPN provider is in a position to monitor and analyze all traffic through the VPN. While traffic is encrypted from the client’s computer to the VPN server, it ceases to be encrypted between the server and the Internet. Those who control the VPN server (the Iranian authorities in the case of Iranian state VPNs) are completely free to observe and analyze traffic.”

Iran has a record of increasing online censorship at sensitive political times. On June 14, Iran will hold its first presidential vote since 2009, when Mahmud Ahmadinejad’s disputed reelection as president resulted in massive street protests and triggered a major crisis in the Islamic republic. Online social media were widely used by citizen journalists to expose the brutality of security forces.

Anderson says that by targeting VPNs, authorities are repeating that pattern.

“In the past, it has always been at politically contentious moments that you see more aggressive disruption of the Internet applied," Anderson says. "So, for example, when there was the currency protest [in] October, we saw jamming of international satellite broadcast and the blocking of Google services and more aggressive throttling of the Internet. So, in fact this was actually kind of predictable.”

Ali-Reza Anghaie, a senior analyst with Wikistrat -- an online consultancy -- says it’s unclear if the current ban will be in place permanently or is a part of a broader experiment in government control.

But, he says, “Regardless, the Iranian government has repeatedly stated it intends to block foreign services increasingly. The end result will be that the sanctioned alternatives will serve a purpose to the state, even if it allows access to external resources.”